If you understand what is electrical resistance you will get the answer to your question. Resistance, measured in units of OHMS (Ω) is an electrical quantity that measures how a device controls the electric current flow through it.

Resistance calculation with Ohm’s law:

R = V ÷ I

R is the resistance

V is the voltage

I is the current

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We have two bulbs, 100 W, and 60 W – I assume the voltage is 234 V 50 Hz single phase A.C. the standard supply in the country.

Next, let’s find out the current drawn by the two bulbs:

100 W ÷ 234 V = 0.43 Amps

60 W ÷ 234 V = 0.25 Amps

Now, find the resistance using Ohms law.

OHM’s law=I=V÷R

You will find the answer.